1. Field of the Invention
The present invention relates to a laminated common-mode choke coil that can be used in various electronic devices.
2. Description of the Related Art
A common-mode choke coil is an electronic component comprising two coiled conductors formed on an insulator and, in particular, a laminated common-mode choke coil is structured in such a way that two spiral conductors are facing each other via an insulator layer. Preferably the insulator layer between the two conductors has a low dielectric constant. Accordingly, glass ceramics is favorably used as the material for this insulator layer. To lower the dielectric constant further, use of silica (quartz) is preferable. In consideration of chemical resistance, etc., however, many common-mode choke coils use not only silica, but also alumina-spiked filler, as the material for glass ceramics.
Patent Literature 1 discloses a laminated common-mode noise filter comprising a non-magnetic layer, two magnetic layers sandwiching the non-magnetic layer, two opposing planar coils embedded in the non-magnetic layer, and external end face electrodes, where it is proposed that, to increase the bonding strength between the external end-face electrodes and magnetic layers, a glass component be contained in the magnetic layers and preferably a glass component be contained also in the non-magnetic layer and base layers for external end-face electrodes.
According to Patent Literature 2, it is proposed that, to increase the impedance of the common-mode component, at least two magnetic layers be provided above and below two coiled conductors, respectively, with two non-magnetic layers provided between the two magnetic layers, while a glass-containing low-dielectric-constant layer be formed between the non-magnetic layers and a glass-containing material of low magnetic permeability be used to form an insulation layer between the two conductors. According to Patent Literature 2, this constitution increases the impedance of the common-mode component because there is a non-magnetic layer between the glass-containing low-dielectric-constant layer and each magnetic layer, which in turn prevents direct contact between the magnetic layer and low-dielectric-constant layer and thereby prevents drop in the magnetic permeability of the magnetic layer.